For an audio speaker, a diaphragm is a core component of the audio speaker and the performance of the diaphragm has great effects on the performance of the audio speaker. In the prior art, different materials, such as paper pulp, polypropylene and metal materials etc., but traditional audio speakers made of these materials have drawbacks in audible sound reproduction. For example, the diaphragm made of paper pulp is sensitive to humidity and the temperature and non-durable; the humidity resistance thereof is bad; the water can be absorbed by it. As a result, the diaphragm made of paper pulp tends to be degraded after being used for a period of time; the wet weather condition accelerates the process of degrading. Meanwhile, the heat resistance of the diaphragm made of paper pulp is bad too, and in high temperature environment, the diaphragm made of paper pulp may be deformed over time. Therefore, the paper cone is sensitive to the temperature and the humidity, and the changes of the using environment may have a certain impact on the sound; besides, the changes of the using environment may cause the paper cone to produce irrecoverable deformations. Therefore, the performance of many audio speakers employing the diaphragm made of paper pulp is degraded after the audio speakers are used for a period of time. Compared with the diaphragm made of paper pulp, the diaphragm made of polypropylene is at lower density and poor in heat resistant. The diaphragm made of metal has a strong rigidity and low resistance and the energy will not be absorbed by the diaphragm itself, so when the paper cone is split, there is an obvious formant at the high point of the frequency response. If not properly handled, the formant will easily lead to “metallic sound”, which means the harmonic distortion may be formed during the process of the sound reproduction.
To overcome these drawbacks, in the prior art there is an alternative solution of using the polyethylene terephthalate (PET) sheet (hereinafter called PET sheet) containing micropores having the average size of 10-30 microns to make the audio speaker diaphragm. The diaphragm made of such solution has a better elasticity level and a lighter weight, which can ensure that the audio speaker diaphragm is durable, and produces less distortion during the sound reproduction process. However, the audio speaker diaphragm made of PET sheet still has the following problems: firstly, during the production, it needs to make sure that the foaming PET sheet is sufficiently foamed, the PET sheet is too thick (the limiting value of the present thickness is 0.85 mm), compared with the existing audio speaker diaphragm with micropores; secondly, the microspores are still too large, which will affect the best adaption between the density level and the rigidity level. Therefore, the foaming PET sheet in the prior art is not recognized as the best material for producing audio speaker diaphragm in industry. For a long time, people have been seeking for new materials to make diaphragms and until now there are still many researchers and research institutions working on it, so the prior art still needs to be improved.